60 Electrical Power Systems Technology
True Power
Apparent Power
Power Factor
Three-Phase Power Analyzer
Power Factor Meter
Power Demand Meter
Average Power
Peak Power
Frequency Measurement
Synchroscope
Phase Sequence
On-Line Operation
Ground Fault Indicator
Megohmmeter
Clamp-on Meter
Telemetering
MEASUREMENT SYSTEMS
All measurement systems have certain basic characteristics. Usually, a
specific quantity is monitored, either periodically or continuously. There-
fore, some type of visual indication of the quantity being monitored must
be available. For this purpose, several types of instruments for measuring
electrical and physical quantities are available. The basic types of mea-
surement systems can be classified as: (1) analog instruments, (2) compara-
tive instruments, (3) cathode ray tube (CRT) display instruments, (4) numerical-
readout instruments, and (5) chart-recording instruments.
Analog Instruments
Instruments that rely upon the motion of a hand or pointer are re-
ferred to as analog instruments. The volt-ohm-milliammeter (vom) is one type
of analog instrument. The vom is a multifunction, multirange meter. Single-
function analog meters can also be used to measure electrical or physical
quantities. The basic part of an electrical analog meter is called the meter
movement and is shown in Figure 3-1. The movement of the pointer along
a calibrated scale is used to indicate an electrical or physical quantity. For
example, physical quantities such as air flow or fluid pressure can be mon-
itored by analog meters.